Researchers find scales on crocodile heads are formed from cracks not genetically defined

(Phys.org)—A research team made up of members from Switzerland, France and Belgium has discovered that the scales on the heads of crocodiles are not arranged due to genetics but come about because of cracking in the skin while the skull is still developing. They describe their research and findings in their paper published in the journal Science.

Scale development in reptiles, the team notes generally comes about due to a process known as scale primordium, where units of development are genetically driven – scales grow in the shape and color that have been described by their DNA. That's the case for crocodiles as well, they write, except for the scales that cover the head, where things are very different. Instead of regular patterns that occur due to scale primordium, there is chaos the researchers found, which led them to wonder if a different development process was at work.

To find out, they took multiple high resolution photographs of the heads of 15 young crocodiles from every angle possible then used computer software to create 3D models made up of just the lines that formed the divisions between the scales. The lines were then analyzed using pattern recognition software and the results showed that the polygons that were created by the lines mimicked patterns seen in natural cracking, such as when mud dries or a pot is broken.

Next, the team studied embryonic development of crocodiles in their lab, watching closely as Dermal Pressure Sensors (DPS) – sensory organs that detect surface water changes – developed as raised bumps or mounds in random fashion over the face, jaws and other parts of the head. Scale primordium never occurred. Instead thick skin developed over and around the DPS bumps. As the skull grew, grooves began to appear between the mounds that eventually became interconnected. As the grooves deepened they began to take on the familiar look of the adult resulting in the scaly look that crocodiles are known for.

This discovery, the researchers say, provides more information to scientists studying the interplay between genetic determination and the physical and/or chemical processes in the environment that together determine the biologic development of organisms.

More information:
Crocodile Head Scales Are Not Developmental Units But Emerge from Physical Cracking, Science, DOI: 10.1126/science.1226265

ABSTRACTVarious lineages of amniotes display keratinized skin appendages (feathers, hairs, and scales) that differentiate in the embryo from genetically controlled developmental units whose spatial organization is patterned by reaction-diffusion mechanisms (RDM). We show that contrary to skin appendages in other amniotes (as well as body scales in crocodiles), face and jaws scales of crocodiles are random polygonal domains of highly keratinized skin, rather than genetically controlled elements, and emerge from a physical self-organizing stochastic process distinct from RDM: cracking of the developing skin in a stress field. We suggest that the rapid growth of the crocodile embryonic facial and jaw skeleton, combined with the development of a very keratinized skin, generates the mechanical stress that causes cracking.

Related Stories

A University of Missouri researcher has identified a new species of prehistoric crocodile. The extinct creature, nicknamed "Shieldcroc" due to a thick-skinned shield on its head, is an ancestor of today's crocodiles. Its ...

(PhysOrg.com) -- Researchers from the Fordham University in New York have uncovered evidence that what the world has looked to as the iconic Nile crocodile is actually two different species of crocodile that are only distantly ...

Crocodiles and alligators are notorious for their thick skin and well-armored bodies. So it comes as something of a surprise to learn that their sense of touch is one of the most acute in the animal kingdom.

Recommended for you

(Phys.org)—That there are universal patterns in the naming of colors across languages has long been a topic of discussion in a range of disciplines, including anthropology, cognitive science and linguistics. However, previous ...

It has been 20 years since Dolly the sheep was successfully cloned in Scotland, but cloning mammals remains a challenge. A new study by researchers from the U.S. and France of gene expression in developing clones now shows ...

(Phys.org)—A team of researchers with members from several institutions in China has calculated what they believe is the minimum amount of land preservation needed to sustain wild giant panda populations. In their paper ...

The differences in how male and female fruit flies resist and adapt to oxidative stress may shed new light on how age-related diseases such as Alzheimer's and Parkinson's affect men and women differently.

0 comments

Please sign in to add a comment.
Registration is free, and takes less than a minute.
Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.